In a conventional method of making such a sealed paper, a sheet of paper to be single- or double-folded has, in a preliminary stage before it is rolled into a paper roll, been treated by applying, in a given pattern, a special adhesive as represented by a pressure sensitive adhesive to one of a pair of mutually opposing surfaces to be found in a web of paper unrolled from the paper roll after it is single-folded to provide a V-shaped cross sectional configuration or double-folded to provide a Z-shaped cross sectional configuration. The web of paper which has a message or information preliminarily printed thereon is unrolled from the paper roll and supplied to a folding machine where it is single- or double-folded as mentioned above. The folded web of paper is then sealed with the pair of the mutually opposing surfaces bonded together with the pressure sensitive adhesive, and thereafter, is cut into a number of sealed paper units each having a given size.
The conventional sealed paper making method described above has been found to be inefficient since it requires a pre-treatment operation in which a special adhesive is applied preliminarily in a given pattern for each individual sealed paper unit. Such pre-treatment operation must be carried out in a separate step on a sheet of paper before it is rolled into a paper roll which, in turn will provide an unrolled web of paper to be folded. The method is also characterized by poor production efficiency because a sealed paper must be made from a paper roll having a required pattern of adhesive preliminarily applied thereto, wherein a web of paper unrolled from the paper roll must, when it is to be folded at a given position, be registered in alignment in a top-to-bottom direction so that the folded web of paper may next be cut into a number of sealed paper units. This has required the web of paper to be synchronously fed at a limited feed rate with a pin tractor. It should further be pointed out that the above mentioned conventional sealed paper making method is disadvantageous in terms of costs coupled with the above noted poor efficiency since it must make use of a special adhesive such as a pressure sensitive adhesive which is expensive.
It is accordingly an object of the present invention to provide an improved method of making a sealed paper, which enables a number of sealed papers to be made with an increased efficiency and which also allows the use of an inexpensive adhesive, to thus make the method less costly.